It is essential in nuclear power reactor operations to remove the radioiodine fission-product and the organic derivatives that are present in the reactor air cleaning systems. This is done by passing the air stream through filters containing adsorbent charcoal which is suitably impregnated with compounds capable of removing both elementary iodine and the organic iodide. The charcoal must remain at high efficiency during its long service time, often when confronted with adverse contaminants in the air.
Two types of chemical reactions have been used in beds of impregnated charcoals for the removal of radioactive iodine and radioactive methyliodide from air streams. One type employs impregnating solutions containing iodine. The removal of radioactive iodine and radioactive methyliodide is considered to be based upon a dissociation-controlled exchange, i.e. the exchange is controlled by dissociation of one of the species. For example, EQU CH.sub.3 I.sup.131 + I.sup.127 -- (on charcoal) .fwdarw. CH.sub.3 I.sup.127 + I.sup.131 -- (on charcoal)
The other type of impregnation entails an association-controlled exchange. The reactants form a labile association complex, the stability of which varies for different systems. An example is the reaction between a tertiary organic amine such as triethylenediamine and radioactive methyliodide. EQU N .tbd. (CH.sub.2 -CH.sub.2).sub.3 .tbd. N + CH.sub.3 I.sup.131 .fwdarw. [N .tbd. (CH.sub.2 -CH.sub.2).sub.3 .tbd. N.sup.+ - CH.sub.3 ] I.sup.-.sup.131